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Fri, 10 Aug 2018 06:27:48 +0000en-UShourly1https://wordpress.org/?v=4.9.8What Are Hydraulic Flow Control Valves And How To Testhttp://www.finotek.com/hydraulic-flow-control-valves-and-testing/
http://www.finotek.com/hydraulic-flow-control-valves-and-testing/#respondTue, 05 Jun 2018 11:20:30 +0000http://www.finotek.com/?p=3614Hydraulic flow valve is simply referred to as flow control valve, and the flow control is achieved by changing the flow area of the orifice. This type of hydraulic flow valve is commonly used in hydraulic circuits and is used in particular to adjust the speed of the actuator. Hydraulic Flow Control Valve Generally Be

Hydraulic flow valve is simply referred to as flow control valve, and the flow control is achieved by changing the flow area of the orifice. This type of hydraulic flow valve is commonly used in hydraulic circuits and is used in particular to adjust the speed of the actuator.

Hydraulic Flow Control Valve Generally Be Classified:

1) Throttle Valve, the hydraulic flow area can only be changed according to external instructions such as manual operation, mechanical or electronic control, so the actual flow through the valve is affected by the pressure difference across the valve.

2) Two-way hydraulic flow control valve, referred to as two-way flow valve, its flow area can change with the pressure difference between the two connection side of the flow valve within a certain range, to keep the flow through constant, so it is also known as pressure compensation (pressure -compensated)

Throttle control, it is often referred to as a speed control valve, in fact, it is sometimes used only to regulate the flow and is not used for speed regulation.

3) Three-way hydraulic flow control valve referred to as three-way flow control valve, the flow chamber of the priority oil chamber and the bypass oil chamber be changed as per the different pressure of each port, to achieve flow regulation, which is not the same processing like the pressure relief valve for speed control.

Hydraulic Flow Valve Function

Because the throttle valve is mostly operated by a cone shape poppet with a very small angle, it is often referred to as a needle valve. It has a simple structure and low cost, and can be completely closed.However, with the improvement of technology, there are some needle valves that are not at all like needles: with a cylindrical spool, which has a regulation indication scale for better flow adjustment precisely.

Hydraulic Flow Valve Types

From a functional classified the hydraulic flow valve can be divided into the following two types:

1) Normal throttle valve. Bidirectional throttling can be realized.

2) One-way throttle valve, which can throttle flow when the oil flows in forward. When the oil flows in the reverse direction, the throttling port is fully opened without throttling.

From the adjustment mode of view, there are fixed and not adjustable, there are manual adjustment, there are also electric proportional adjustment of screw-in cartridge flow valve.

Hydraulic Flow Valve Application

The A throttle valve is used as an inlet throttle to control the speed at which the hydraulic cylinder overcomes resistance while the cylinder rod in and out.
The use of two one-way throttle valves at port B serves as an outlet throttling to prevent the cylinders from moving too fast.

Hydraulic Flow Valve Functional Principle

The two-way hydraulic flow valve is actually formed by connecting two throttle ports in series. One does not being changed with the pressure of the inlet and outlet, is called fixed throttle port, also called flow sensor, referred to as throttle valve. The flow area of ​​the other throttle orifice changes with the pressure of the inlet and outlet, that is, the constant pressure difference valve.

The pressures p2, p3 of the throttle valve are setting at both ends of the constant pressure differential spool. The poppet moves under these two pressures and the spring force and stops at the equilibrium position, so that between these two pressures, the difference, that is, the pressure difference across the throttle valve, maintains the constant-spring pressure. In this way, the flow through the valve can be kept relatively constant, independent of the pressure of the valve.

When the oil reverses ②->①, it is like a throttle valve. Because, at this time, due to p2<p3, the constant pressure differential valve poppet will move to and stay at the left end side under the action of the spring force, and the valve port will be fully opened and the flow regulation is not being adjusted at the moment.

Type Of Hydraulic Flow Valves

Constant pressure differential valve can be pre-positioned or post-positioned installed in hydraulic system. The threaded plug-in two-way flow valve is mostly set at a constant pressure differential.

In terms of driven characteristics, the front-mounted type is more suitable for inlet throttling flow control, and the rear type installation is more suitable for outlet throttling flow control. Because of this, the constant pressure differential valve can response to the changes in the load pressure earlier and react faster.

In addition to the adjustable orifice, there is also a throttle orifice that can not be adjustable, but a constant pressure differential spring pre-tightening force is adjustable

Because, when the oil is reversed flowing, the normal two-way hydraulic flow valve operates like a general throttle valve. Therefore, in order to reduce the flow resistance, there is also a valve with a reverse flow check valve. There is also an electric proportional type flow control valve, which can be adjusted by electric signals.

Area I: The pressure difference between the two ends of the valve, p0-p2 is lower than the spring presetting pressure, and the constant pressure difference is fully open. The entire valve is a throttle valve. Therefore, the two-way hydraulic flow valve has a minimum working pressure difference ΔP min, which is approximately in the range of 1.2 MPa to 3 MPa.

Below this pressure difference, the flow cannot be maintained without being affected by the load pressure.

Area Il: Work area. The pressure difference across the valve is higher than the minimum operating pressure differential. The constant pressure differential valve is partially closed, which can serve to consume pressure and maintain a constant differential pressure. The bigger of the pressure difference between the two ends of the valve is, the smaller the valve of the constant pressure difference valve is closed and the corresponding spring force is increased. As a result, the pressure difference between the two throttle valves becomes bigger, and the flow rate increases. On the other hand, the bigger of the flow rate, the bigger of the hydraulic force on the spool, which in turn reduces the pressure differential.

Therefore, the slope of the characteristic curve is determined by both the spring force and the hydraulic force. Generally, it rises when the flow rate is set low, and it drops when the flow rate is set high.

Area Ill: The pressure difference is so large that the constant pressure differential valve has moved to the stroke end and it is no longer possible to maintain a constant differential.

Hydraulic source. The output flow must be bigger than the test range and should be smooth. If necessary, setting an accumulator at the pump outlet

Relief valve for loading. The adjustment range must be bigger than the test range

Pressure gauges for monitoring purposes.

Thermometer

Pressure sensor. The conditions for using the inlet pressure to replace the difference between the inlet and the outlet: the piping to the outlet tank is short and thick, so that the display value of 3b is negligibly small relative to 3a. Otherwise, a pressure sensor should be added at 3b.

Connect the recorder: flow qy7 as the Y axis and pressure p5 as the X axis. To make the oil temperature reach the predetermined value, usually choose No. 32 hydraulic oil, at 40 °C.

2) Test procedure

Open relief valve 2 to maximum to minimize pressure. Turn on the hydraulic power source.

The tested valve 6 is adjusted to a minimum value for the flow adjustment range.

Start recording. Slowly close the pressure relief valve 2 and increase the pressure p5 to reach the maximum test pressure. Then slowly open the pressure relief valve until the pressure p5 is at its lowest point. Pause the record.

]]>http://www.finotek.com/hydraulic-flow-control-valves-and-testing/feed/0What Are Hydraulic Solenoid Valves And How To Testhttp://www.finotek.com/hydraulic-solenoid-valves-and-testing/
http://www.finotek.com/hydraulic-solenoid-valves-and-testing/#respondTue, 05 Jun 2018 11:20:28 +0000http://www.finotek.com/?p=3613Hydraulic solenoid valve can open and close one or more flow channels by energizing and de-energizing the solenoid, usually there are modular hydraulic solenoid valves and cartridge solenoid valves installed in the hydraulic system or equipment. The 2/2-way hydraulic solenoid valve type has a much more connected form in the de-energized condition than the

The 2/2-way hydraulic solenoid valve type has a much more connected form in the de-energized condition than the modular solenoid valve.

Hydraulic solenoid valve, from the point of view of the structure of the main valve spool, only two position, two-way and two position and three-way seat valve are spool with seat valve, the other are all spool valve.

The valve spool and spool seat are generally made of steel and hardened to achieve long life. However, there are also individual varieties that use softer seats in order to meet the strictly requirements for internal leakage in certain applications.

From the internal structure, the hydraulic solenoid valve can be divided into direct-acting and pilot differential. In general, only the two-way type and the three-way valve in the hydraulic solenoid valve have a pilot type that is electrohydraulic control, and the other types are direct-acting spool valves, that is, electric control. For simplicity and ease of comparison, the graphical symbols do not distinguish between electrically and electro-hydraulic valves.

The solenoid coil converts the input current into a magnetic field. The armature sleeve assembly converts the magnetic force into a pulling force or thrust force in a magnetic field. The hydraulic solenoid valve parts assembly utilizes this force to overcome the spring force and the liquid force, to opens or closes the corresponding flow channel. The solenoid coils are fixed with nuts for easy replacement.

The steady state characteristics of the hydraulic solenoid valve are mainly examined from the differential pressure flow characteristics and working range.

The steady state characteristics of the hydraulic solenoid valve are mainly examined from the differential pressure flow characteristics and switching limit.

Differential Pressure Flow Characteristics And Test Of Hydraulic Solenoid Valve:
Differential pressure flow characteristics:
From the differential pressure flow characteristics of the hydraulic solenoid valve, it can be realized that there will be much pressure loss when a certain flow rate is passed.

Because the direct-acting solenoid valve is an on-off valve, in normal operation, there are only two states that are off and on. Unlike a continuous regulating valve, there is an intermediate state. Therefore, the differential pressure characteristic curve of a certain channel is usually a parabola.
Pilot solenoid valves are different. Its main port is gradually opened at a relatively small flow rate. Therefore, this is not completely parabolic.

Many hydraulic solenoid valves have multiple different channels when de-energized or energized, and the flow resistance of these channels varies. Therefore, to fully express the pressure differential flow characteristics of hydraulic solenoid valve often requires multiple curves.

A hydraulic power source. Its output flow rate should be adjustable. The maximum flow rate should exceed the estimated nominal flow rate. The minimum flow rate is not necessarily small, generally as long as the corresponding pressure difference is less than 0.1 MPa. Because, the differential pressure flow characteristics of solenoid valves at very small flow rates are generally not the focus of attention. Variable hydraulic pump can be used, in order to reduce the flow fluctuations, an accumulator can be added if necessary.

A pressure relief valve. For safety protection only, the set value should not exceed the allowable pressure of the testing valve.

A flow sensor. Generally, the maximum and minimum flow ratios are 10 or more.

The testing valve

A thermometer.

A pressure sensor.
6a. Measures the inlet pressure. 6b, 6c. Measure the pressure at ports A and B separately.
If the pressure at the outlet T cannot be ignored, a pressure sensor should also be provided.
Because of the measurement range of the differential pressure flow curve, 1 to 2MPa is sufficient. Therefore, the pressure sensor should Choose a small range for higher measurement accuracy.

X-Y recorder, or digital oscilloscope, or computer-aided test system, used to record the steady state characteristics.

(2) Test process

1) Preparation stage

Connect the X-Y recorder: The output qv3 of the flow sensor 3 acts as the X axis.

Allow the oil temperature to reach the predetermined value, and use the VG32 hydraulic oil, and maintain the temperature at 40°C.

The flow of hydraulic power source 1 is minimized.

3) Test procedure

The testing valve is switched to an open position. The difference in the output of the corresponding pressure sensor, for example p6a-p6b, or p6a-p6c, is the Y-axis of the X-Y recorder.

Start recording.

Slowly increase the flow of the hydraulic source until the pressure difference exceeds, say, 1 MPa

Slowly reduce the flow of the hydraulic source to a minimum.

Stop recording.

The recorded is pressure difference flow characteristic curve of the corresponding channel.

According to the need, change the pressure sensor output, or change the valve connection, repeat the process b.

The allowable pressure of common hydraulic solenoid valves in the market is mainly two levels: 21MPa (20.7MPa) and 35MPa (or 34.5MPa). But there are also 24MPa, 25MPa and 28 MPa, etc.

Hydraulic solenoid valves with different allowable pressures use different materials and characteristics for their components, since the manufacturing precision and manufacturing process are different, the price will naturally be different accordingly. Therefore, the high allowable pressure cannot be purchased in no target.

The permissible pressures at all outlets are generally the same except that individual T outlets are lower. However, whether or not it can work and switch reliably under this pressure depends on the operating range curve.

Switching Limit Curve

The spool switching limit of the hydraulic solenoid valve is that the solenoid valve can be reliably held in a certain working position within this range and reliably switched to another working position. If the actual operating parameters exceed this range, the switching speed may slow down, may not even switch at all, or may not be maintained in the normal working position.

The spool switching limit curves given on the general product samples are made under ideal laboratory conditions: clean mineral oil, oil temperature 40°C, viscosity 32mm, input voltage is 90% of the rated voltage. If the actual working conditions fluctuate greatly, they should be conservatively selected.

Factors That Affect The Switching Limit Of Solenoid Valve

The factors affecting the switching limit of the solenoid valve are different in the direct acting type, the pilot differential type, the spool valve and the poppet seat valve.

Direct-Acting Spool Valve: The factors affecting the spool switching range of the direct-acting spool solenoid valve is mainly the solenoid force of the coil, the spring force, the static pressure of the pressure medium to the valve spool, the hydraulic force and the friction force.
It is the electromagnetic force that causes the spool to switch to or remain in the energized position. The electromagnetic power of the hydraulic solenoid valve is generally between 14-30W, and the electromagnetic force is very limited, about 70-120N.Retaining the spool or returning to the de-energized position is the return spring force. The spring force must be sufficient to overcome the maximum value of the hydrodynamic force.

The side port oil fluid balances the static pressure of the valve spool. The liquid pressure on the slide valve spool at the end face port is balanced with each other through the hole in the valve spool, or it can only be connected to the T port.
Impeding the movement of the spool from one working position to another, or deviating the spool from its working position, is the spring force, the combined force of the static pressures of the chambers, and the hydraulic force that is approximately proportional to the flow rate and flow speed.

The hydraulic power reaches a maximum at small openings, that is, in a transitional state.
The valve spool and valve hole manufactured by Finotek have normal fit size and shape position deviation, and when immersed in clean hydraulic oil, the friction force is generally small relative to solenoid force and spring force and can be ignored.

Pilot Differential Valve: The pilot type and the pilot differential type valve is usually very small, the flow rate is very small as well, the fluid power is also very small. They are generally poppet valves with static pressure imbalance. As long as the solenoid force overcomes the spring force and static pressure, the pilot valve core can be removed.
The main factors affecting the working range of the main valve are: spring force, static pressure of the hydraulic oil on the valve spool, and hydraulic power.
The difference between the static pressures at both ends of the main spool overcomes the spring force and the hydraulic force, pushing the main spool and opening the related chamber. Since the difference in static pressure and the area of ​​action can be much larger than the electromagnetic force, the working flow rate of the pilot differential valve can be much larger than the direct-acting type.

Testing Of Hydraulic Solenoid Valve Switching Limit

For the determination of the switching limit of the solenoid valve: ISO 6403:1988 or refer to the GB/T 8106-1987 standard version

Test loops

Hydraulic source. Its output flow is adjustable. Variable pumps can be used. In order to reduce the flow fluctuations, an accumulator can be added if necessary

Relief valve. 2a as a safety valve, its set value should be the allowable pressure of the valve under test. 2b, 2c simulated load, the set value should be lower than the allowable pressure of the valve under test

Flow sensor

The Tested Valve

Check valve

Temperature sensor.

Pressure sensor. The inlet pressure is measured at 7a, and the pressures at ports A and B are measured at 7b and 7c, respectively.

Test Procedure

The solenoid coils are pre-powered until the balance is reached. Input voltage: 90% of rated voltage.
The spool of directional valve can move in at least 6 full strokes in both directions.
If the hydraulic directional valve cannot be normally switched, reduce the pressure or flow. On the coordinate paper, with the horizontal axis of the flow and the vertical axis of the pressure, the normal working points are marked.
Finally, connecting the boundary points results in the valve’s working range.

]]>http://www.finotek.com/hydraulic-solenoid-valves-and-testing/feed/0What Are Hydraulic Pressure Relief Valves And How To Testhttp://www.finotek.com/hydraulic-pressure-relief-valves-and-testing/
http://www.finotek.com/hydraulic-pressure-relief-valves-and-testing/#respondTue, 05 Jun 2018 11:20:20 +0000http://www.finotek.com/?p=3612Modular hydraulic pressure relief valve and hydraulic cartridge pressure relief valve are available in almost all hydraulic systems, so it is important to have a full and deep understanding of the characteristics of the relief valve used. Hydraulic Relief Valve Function and Application Hydraulic relief valve consists of valve housing A, valve poppet B and spring

Hydraulic Relief Valve Function and ApplicationHydraulic relief valve consists of valve housing A, valve poppet B and spring C and other basic components, at least there are one inlet (P) port and one outlet (T) port. The main role of hydraulic pressure relief valve is essentially pressure limiting: to limited the working pressure is by pressure relief.
The load determines the pressure, the hydraulic relief valve only limits the pressure of the hydraulic system, but the pressure relief valve itself cannot generate pressure.

Basic Common Features Of Various Types Of Hydraulic Pressure Relief Valves:1) When the inlet pressure reaches the pressure presetting point, the pressure relief valve will open and relief the pressure then.
2) The spring chamber is generally connected to the outlet port and the back pressure is equal to the outlet pressure. Therefore, in addition to the type of unloading outside, the pressure at outlet port is directly increased by 1:1 proportion. If you want the opening pressure to be completely independent of the outlet pressure, you should consider using a sequence valve.

Basic Functions Of Hydraulic Relief Valves:
A. As a safety valve used to limit the maximum pressure of hydraulic system, it plays the following role:
1. Avoid the high pressure damages to the hydraulic system, components and piping
2. Avoid hydraulic power source such as electric motors, diesel engines, or gasoline engines stops while operation due to heavy loads
3. Avoid excessive force/torque generated by the hydraulic cylinder or hydraulic motor, which may damage connected or pushed components; Avoid hydraulic cylinder or hydraulic motor with large inertia load, due to excessive inertial force during acceleration braking or torque, resulting in damage. In these operating conditions, the pressure relief valve is normally closed.

B. As pressure control valve, hydraulic pressurepressure relief valves maintain the pressure in whole hydraulic system or partial system within a specific level or range, for example:
1. Relief flow for the inlet and outlet throttling speed control circuit, which can be referred to as the constant pressure valve at this time
2. Generate the back pressure on the return oil to improve motion stability, which is often referred to as back pressure valve.
3. Unloading the pressure in double pump circuit or accumulator circuit, which is often referred to as pressure unloading valve.In these conditions, the hydraulic pressure relief valve is normally open.

There are many types of hydraulic pressure relief valves, which can be classified from many different angles.Classification according to valve poppet structure:
1) Ball type: The ball type relief valve is simple in structure and low in cost, but it is only suitable for small flow.2) Poppet type: The poppet hydraulic pressurerelief valve can pass through a large flow, with less leakage, quick response and longer life, it is most widely used.3) Spool type: The spool type relief valve can flow through a larger volume but with a smaller pressure range regulation.

Classification According To The Type Of Action
1) Direct acting pressure relief : The direct-acting type has fast response and small overshoot and is suitable as a safety valve to reduce the impact, but the pressure regulation deviation is large, that is, the control pressure fluctuates greatly with the flow rate.2) Pilot operated pressure relief: The pressure regulation deviation of pilot type is small, control pressure accuracy is high, and it is used in occasions where pressure control is more accurate needed, but the response is slower3) Soft pressure relief type : Soft pressure relief type will be able to relief the pressure before the pressure reaches to presetting value and surges in the inlet port.
The pressure relief valve in the constant rate pump with the open central spool directional control valve, or the (constant pressure) variable pump with the closed neutral directional control valve circuit generally requires a low leakage, fast response, anti-pollution, vibration reduction, can be considered using direct-acting type.
In the hydraulic constant rate pump throttle circuit, continuous flow supply and high-precision pressure control are generally required. When small amounts of internal leakage have little effect, pilot type pressure relief valves may be considered.

Classification According to the location of the application in the loop1) Main hydraulic pressure relief valve, installed in the same direction of directional valve, the side of the hydraulic pump
2) Secondary hydraulic pressurerelief valve mounted after the directional valve, the side of driving device

Classification according to function

1) Normal type2) Pressure-safe type. After opening, it will not be closed until the inlet pressure drops to zero. Not suitable for circuits that require load holding.3) With reverse check valve type. The general relief valve does not pass in the reverse direction.4) Bi-directional type. In the hydraulic motor drive circuit, the pressure relief valve, or a two-way relief valve, should generally be installed on both sides to prevent excessive pressure on one side due to external loads during neutral conditions.5) External control type. The opening pressure can be changed by an additional control type such as a hydraulic control, air control, a solenoid switch, or an electrical proportional control.
* There is also a so-called thermal protection relief valve. Actually, it is a small direct flow relief valve that is used as a safety valve. It starts to relief the pressure when the temperature rises causing thermal expansion of the closed liquid to protect the components (mainly hydraulic cylinders) from high pressure damage.
From the point of oil connection, ordinary types are two-way. The three-port and four-port ports are generally available for external control.

Differential Pressure Flow Characteristics Test For hydraulic pressureRelief Valve
(1) Test circuitSee the figure according to 1S003:1988 and GB/105-19871. Hydraulic power source. It is required that the flow rate be smoothly adjustable throughout the test range, which is difficult to achieve with a single variable pump or a fixed pump with a speed control valve. Especially in the initial stage, because the required flow rate is very small, it is often below 0,1 L/min. Using multiple speed control valves in parallel, or bypass throttle valve can take in to consideration.2. The pressure relief valve in the system is used for safety protection only. The pressure set value must be higher than the test range, but it does not exceed the allowable pressure of the valve under test.4.Thermometer5. Pressure sensor. 5a measures the inlet pressure. 5b measures the outlet pressure. If the outlet pipe is very short, thick, the pressure loss is negligibly small even can be omitted. Or only by a low pressure gauge is used for monitoring.6. Tested valve7. Flow sensor. Gear flow sensors may be considered here because they have a much larger measurement range than turbine flow sensors.8. X-Y recorder, or digital oscilloscope, or computer data acquisition record display system.

Test procedure:1. Turn on the hydraulic pressure source
2. The tested valve 6 is adjusted to the minimum value of the given pressure adjustment range.
3 start recording. Slowly increase the output flow of the hydraulic source from zero to the maximum test flow, then slowly decrease it to zero and stop recording. 4. The tested valve 6 is adjusted to the maximum value of the given pressure adjustment range and the steps are repeated step 3.
5. Set a few more values between the maximum and minimum values of the pressure adjustment range and repeat step 3.
*Keep the oil temperature relatively constant throughout the test. The test curve thus obtained is the valve’s characteristics under the operating conditions of the valve, which is typical test curve.

Hydraulic power source. It is best not to use a variable pump to avoid the dynamic response characteristics of the variable mechanism affecting the test results.

The system pressure relief valve is for safety protection only. The pressure presetting value must be significantly higher than the test range. Pressure relief should not occur during the test, otherwise it will reduce the system pressure rise gradient.

Bypass valve. Where 3a is used for pressure loading, it must be a quick-response valve, otherwise it will not be able to obtain a sufficient gradient of system pressure rise. 3b is used to control the pressure in the pilot chamber of an externally controlled relief valve. This part of the circuit must be modified accordingly with the type of valve being used.

Thermometer.

Pressure sensor. Response characteristics better than 5000Hz

The valve being tested.

Flow meter. If the flow is known, it can be removed or moved to the return line of the tested valve in order to reduce the volume of the pipe.

Throttle valve. Set initial pressure.

Zero flow display. It is used to monitor whether the flow bypasses the test. It can be a measuring cup or an ordinary container.

Quick recorder. If digital, sampling time is shorter than 0.2ms.

Testing Process:
Preparation:
1. Connect the pressure sensor output P5 to the quick recorder.
2. Start the hydraulic power source. Allow the oil temperature to reach the predetermined value.
3. The tested valve 6 under is adjusted to a certain opening pressure.
4. Bypass valve 3a open. Using the throttle valve 8 to set the initial pressure, it should approach but not exceed the opening pressure of the valve 6 under test.Test Procedure:
1. At the beginning of the test, the flow from the hydraulic power source 1, is directly drawn through the bypass valve 3a and the inlet pressure P5 of the valve under test is lower than the opening pressure and is closed by the tested valve 6 .

2. Quickly close the bypass valve 3a, P5 quickly rises, open the tested valve 6. After a while, P5 has stabilized. By recording the transient changes in pressure P5, the transient behavior of the tested valve will be able to be seen.

3. If the pressure in the pilot chamber of the tested valve is externally controlled, the bypass valve 3b can be quickly connected to make the measured 6 unloaded. P5 quickly decreased, which can measure the transient characteristics of the tested valve when unloading the pressure

]]>http://www.finotek.com/hydraulic-pressure-relief-valves-and-testing/feed/0What Are Hydraulic Check Valves And How To Testhttp://www.finotek.com/hydrauilc-check-valves-and-testing/
http://www.finotek.com/hydrauilc-check-valves-and-testing/#respondTue, 05 Jun 2018 11:20:18 +0000http://www.finotek.com/?p=3615There are two installation types of hydraulic check valves modular hydraulic check valves and cartridge check valves. Hydraulic check valves also known as one way hydraulic check valve or isolated check valve, allow only fluid flows in one direction and stops the fluid flow from the other direction. Hydraulic check valve can be divided

There are two installation types of hydraulic check valves modular hydraulic check valves and cartridge check valves.Hydraulic check valves also known as one way hydraulic check valve or isolated check valve, allow only fluid flows in one direction and stops the fluid flow from the other direction.
Hydraulic check valve can be divided into two major categories: normal check valve and pilot operated hydraulic check valve by the functional point of view check valve are two-port valves, pilot-operated check valve is a three-port valve, the pressure of the additional control port can control the on or off of the hydraulic oil in the main chamber.

Hydraulic check valve is generally composed of a check valve housing, a spring and a valve poppet, and a non-spring check valve is rarely used. According to the recommendations of ISO 1219-1:2006, the symbol of the function of the hydraulic check valve should be as shown in the figure:
In the graphic symbol of the general one-way valve, the spring is often abbreviated.
When the pressure at port ① is higher than the pressure at port ② plus spring pressure, the valve poppet is pushed open and the oil flow passage is opened, then the oil flows positively through the hydraulic check valve (①->②).
When the pressure at port ② is higher than the pressure at port ①, the valve poppet is pressed against the valve seat by spring force and hydraulic pressure, and then the flow is cut off.

Hydraulic CCheck Valves Are Used In Many Hydraulic Systems:1) Hydraulic check valves are used to protect the heat exchanger and avoid overpressure when the heat exchanger is blocked. At the same time, the heat exchanger can also be bypassed: only a part of the liquid passes through the heat exchanger. The flow rate depends on the opening pressure of the hydraulic check valve and is less affected by the total flow.
2) The hydraulic check valve is used to maintain the pressure in the accumulator. Port ① is the filling port. If it is not filled, the check valve can close this port. In this way, the accumulator pressure will not be lost.
3) The hydraulic check valve is used to make the hydraulic motor variable in both directions at different speeds. If port ② is filled with oil, all pressure oil will flow to the motor due to the function of the check valve closing. If port ① is filled with oil, part of the pressure oil is bypassed through the two-way regulator flow valve and check valve. The speed of the hydraulic motor in this direction will be lower.
4) The check valves with higher opening pressure are also used as low pressure relief valves. There is no essential difference between the structure and function of the two.

Hydraulic check valve can be divided into one-way screw-in type and plug-in type according to the different installation methods.
The plug-in type (Like Logic Valve) is a hydraulic check valve installed inside the cavity of integrated valve block. It is not exposed outside the valve block, this plug-in valve completely enters the inside of the valve block. The screw-in type uses its own thread or other components, such as pipe joints and O-ring rings to installed in the valve block. General depth is as per the valve and bloc calculated before design. According to the different valve poppet, hydraulic check valve can be divided into ball valve poppet type, spool poppet type and spool type.

From the structural point of view, there are flow from the end face, but also from the side flow. This can sometimes simplify the design of hydraulic manifold chamber and reduce the pressure drop.
In addition, there are some additional features of hydraulic check valve, such as with reverse relief valve type. If the hydraulic check valve installed in the hydraulic cylinder that can be used to support the foot of a mobile machine can hold pressure but not over-pressure.
In general, an excellent hydraulic check valve should have small forward flow resistance, rapid reverse closure, reliable sealing, and long life.

Hydraulic Check Valve Flow Differential Pressure Characteristics And TestingIn the way of forward flow, because the pressure drop caused by the spring force and the friction force between the valve housing and the valve poppet needs to be overcome, the through-flow pressure drop cannot be less than the opening pressure.
In order to obtain smaller flow losses, the spring should be as long and soft as possible. In this way, after opening the check valve, the flow increases, the opening increases, and the spring is compressed, the spring force does not rise too quickly.
The flow differential pressure curve for a hydraulic check valve with opening pressures of 0.34 bar and 2.10bar, respectively.
Test circuit diagram as per ISO6403 the recommended test circuit:

Hydraulic power source. The maximum output flow is at least greater than the nominal flow of the test check valve being tested. It is required that its flow should be smoothly adjustable throughout the test range

A relief valve, as a pressure loading valve

Shut off valve (not necessary)

Testing Valve

A pressure gauge or pressure sensor
5a. Measure the pressure at inlet port
5b. measures the pressure at the outlet port. If the outlet pipe is very short and thick and the pressure loss is negligibly small, it may not be necessary to monitor it, to install a low-range pressure gauge only

A thermometer

A flow sensor

X-Y recorder

Hydraulic Check Valve Testing PreparationConnect the X-Y recorder: Flow qv7 is input as the X-axis, pressure difference p5a-p5b or pressure p5a as Y-axis. Allow the oil temperature to reach the predetermined value. Usually choose 32 oil, 40 °C. Adjust the relief valve, release to maximum loose condition, and pressure gauge should show no pressure at the moment.

Hydraulic Check Valve TestingTest Procedure1. Turn on the hydraulic power source (The electric motor drives the hydraulic motor to establish the pressure)
2. Start recording.
Adjusting the pressure relief valve 2 slowly turn the regulation know, increasing the pressure p5a slowly and the flow qv7 increases to the maximum flow. Then slowly open the pressure relief valve 2 to reduce the pressure to zero.
Stop recording.

Cracking Pressure And TestingCracking pressure refers to the pressure in the inlet cavity when the valve poppet is just opened. It is generally between 0 and 2.5 MPa.
The opening pressure of hydraulic check valve is slightly higher than the spring preload pressure.
Check valves are generally spring installed. The spring preload generally exceeds the weight of the spool at least. To ensure that, regardless of the direction of one-way installation, the spool can be reset.
Sometimes harder springs are used to ensure that the spool or poppet will be able to close quickly, or to achieve better compact performance, to ensure a certain opening pressure.
But the opening pressure can theoretically be calculated based on spring preload and effective area, accurate is not so easy actually.

Proposed ISO6403 Check Valve Testing Circuit1. A hydraulic power source. As long as the flow is larger than the opening flow.
2. A relief valve, for establishing pressure. (Because the opening pressure of cartridge check valve is mostly low, in the 0~0.2Mpa range, if there is no pressure valve that can work in this range, use the throttle valve then)
3. A shut-off valve (Not necessary)
4. Testing Valve
5. A pressure gauge
6. A thermometer
7. A flow meter. Actually, when the valve is turned on, the flow rate is very small, the flow it cannot be accurately measured with an ordinary flow meter. If there is no appropriate micro flow meter, just consider using a measuring cup and stopwatch instead.

ISO6403 Test ProcessA. The relief valve (throttle valve) 2 is fully released. Power on the hydraulic pump 1, at this time, there should be no flow at the outlet of the tested valve
B. Slowly close the relief valve (throttle valve) until there is a small flow at the outlet of the tested valve, about 5 drops/sec.
C. At this point, the pressure gauge shows that it is the opening pressure of the valve.

Internal Leakage Testing Of Hydraulic Check ValveInternal leakage means the amount of leakage through the sealing surface between the valve poppet and the valve seat when the hydraulic check valve is in the working condition of reverse sealing (Reverse Flow).
For hydraulic check valve, the internal leakage should generally be as small as possible, preferably without leakage.
The standard for internal leakage is mL/min. However, because of the small amount, therefore, often expressed as drops/min. and 1 mL of mineral oil is about 16-20 drops.Internal Leakage Direct Measurement

A hydraulic power source. As long as the flow rate is significantly larger than the maximum amount of leakage

A pressure relief valve, for establishing pressure

A shut-off valve, not necessary.

The valve being tested.

A pressure gauge.

A thermometer.

A flow meter. However, as the leakage flow is usually very small, it cannot be accurately measured with an ordinary flowmeter. If there is no appropriate micro flow meter, you can consider using a measuring cup and stopwatch instead of the flow meter.

2) Test process

The relief valve 2 is fully loosened before testing, then turn on the hydraulic pump 1 to adjust the relief valve to the testing pressure.

After the leak oil has stabilized, use a measuring cup and stopwatch to measure the amount of leakage in a certain.

Compressed Air Testing Measurement

An excellent hydraulic check valve, should be no leak in a few minutes, often too slow to use the cup. Therefore, there are also compressed air inspections, which can be used as factory inspection. Not suitable for formal testing.

BM10SN hydraulic bar manifold, CETOP5, NG10/Size10, D05 valve series circuit normal flow manifold is complied with the standard NFPA5 valve pattern. There is only a one P inlet and T outlet port on each side and connected with each other while the P and T port on valve mounted is connecting, which is call series circuit type manifold block.

There are only less than 4 valves stations mounted available on the D05 hydraulic manifold block, one valve blocked will stop the fluid flow in the manifold chamber, therefore this manifold is not available for more than 4 valves installation and much valve quality requirement for this series function of hydraulic manifold block.

BM10PX high flow NFPA hydraulic manifold, D05, NG10, Size10 valve parallel circuit extra high flow with X & Y ported manifold is standard valve installation for mounting modular NFPA05 valve pattern. The T port is larger more than 40mm for extra fluid flow rate while drain the system pressure to oil tank, in order to prevent back pressure in hydraulic chamber.

D05 High flow NFPA manifold is usually used in the hydraulic system where requires big fluid flow and quick response of hydraulic actuators, its application in hydraulic pressing machines or large hydraulic cylinder control systems. This manifold is acceptable to below modular valve brand as standard NFPA mounting pattern:

BM10PU hydraulic bar manifold, CETOP5, Size10 valve parallel circuit ultra high flow bar manifold is parallel circuit type ultra high flow hydraulic manifold, the BM10PU hydraulic bar manifold is only available for raw materials of high strength of carbon steel due to large flow rate with large threaded and port.

By using the high quality of carbon steel of manufacturing the high flow parallel manifold to make sure there is no any crack inside the raw materials. There are different steel surface treatment available for this manifold: block galvanization, silver zinc plated, or spray plating treatment for anti-corrosive or good looking purpose.

Pressure relief hydraulic manifold is usually produced in steel or alloy aluminum which is for medium and high pressure. The valve pattern for D05 is standard, comply with international valve mounting pattern standard, it is easy interchangeable for different brands of modular valves, please check the most brand mounted below.

Hydraulic manifold D05 is installed with standard NG10 directional valve to control hydraulic cylinders in various hydraulic press machine or hydraulic systems. The four valve port A, B, P T are each through with relative connection port and isolated to each port, the P port is as inlet port and T port is drain port connecting with hydraulic oil tank.

D05 High flow hydraulic manifold is standard manifold used for mounted with standard CETOP5 directional valve, with valve station from 1 to 7 numbers or more. The T drain port is larger than the inlet port P, in order to drain the pressure quick through T port.

There are internal and external ports X, Y designed with the manifold, which available to connect with SAE or BSPP threaded. The surface of valve mounting reaches to 0.8 in order to seal closely with valves.